A household sewage treatment system not using a municipal sewer typically employs a septic tank and drain field. Household waste is discharged into the septic tank, where solids are allowed to settle, so that liquids may flow to a drain field of perforated conduits that permit the liquid to seep into the ground. To prevent the drain field system from being clogged by solid material that may escape the septic tank, a perforated filter normally is connected between the tank and the field. Such filters generally reside in the tank, in an outlet pipe leading to the drain field. Filters are generally removable, to allow their occasional replacement or cleaning prior to becoming clogged.
When a filter is not periodically replaced or cleaned, it eventually becomes significantly or fully clogged, waste flow into the septic tank exceeds the outflow rate, causing the tank to overfill. The homeowner becomes aware of this by the failure of waste drains to drain at an adequate rate, or at all. In this condition, the filter should be replaced to allow liquids to depart the septic tank. However, a homeowner seeking relief from the inadequate drainage problem may ill-advisedly remove the filter without replacing it, permitting solids to enter and clog the drain field. Such clogging can necessitate an expensive restoration of the drain field, including removing and replacing surface landscaping.
Even in circumstances in which a replacement filter is available, the replacement process may be messy, or allow some solid material to reach the drain field. When a clogged filter is removed, fluid pressure may cause the fluid to overflow the filter housing, or to carry solids to the drain field before a replacement is installed.
An existing system that addresses these issues is PL-122 effluent filter system from Polylok, Inc, of Yalesville, Conn. This system has a floating ball captured in a molded filter housing. When no filter is installed, the ball floats against a seat to close or restrict the housing inlet. When the filter is installed, it pushes the ball down from the seat, allowing flow through the filter. This system has certain disadvantages. First, the filter housing is relatively complex, requiring production by a molding process that limits the housing to use with only one size of filter. While filters may come in different sizes for different applications, many will not fit into a given molded design. Too-long filters will not be fully installable, and too-short filters will not actuate the ball float to permit fluid flow. In addition, this system is susceptible to premature clogging by rising solids that may float up from the bottom of the tank, caused by decomposition gasses buoying the solids. When these solids enter the unprotected inlets of the system, they may lead to premature clogging of the filter. In addition, molded housings are bulky to ship and stock and costly to produce.
The embodiment disclosed herein overcomes these disadvantages by providing a wastewater filtration system with a housing provided by a cylindrical conduit forming a filter chamber and having an inlet end and an outlet. A shutoff valve assembly is connected to an inlet end of the housing, and includes a closure element movable between an open position and a closed position. The closure element is biased to the closed position in the absence of a filter in the chamber and positioned near the inlet such that the shutoff valve opens when a filter is installed. The closure element may be hinged to the housing, and may be counterweighted or spring biased to the closed position.